DH Gipsy engine 1/4 scale

[kendo57]

I made the cam followers from silver steel and the bushes from Bronze, the followers are
placed in from the outside just to show them in the pic



I can now start to build the engine up
Camshaft



Crankshaft



Cylinders plus studs

[kendo57]

Pistons , this one needed a little fettle



The sump was fitted and I needed to turn some bearing races for the front of the crankshaft





Timing gears , the intermediate gear has a shaft containing a bevel gear to drive the magneto



Cylinder heads



Timing up the cam

[iansoady]

Great stuff! Did you make the gears?

[kendo57]

Fantastic stuff This thread is the first thing I check when I log in
What are you going to do with it when it runs? Is the engine build the whole point or wil you build a 1/4 scale Moth to put it in?

Hi ,, I did not make the gears for this , they are all off the shelf just needed machining for
thickness and the bore putting in. I have made gears for my other projects , not difficult if
you have a cutter , the problem is you generally need a cutter for each gear and they can be
expensive so makes sense to buy a gear if you can.
No plans for this engine , hopefully I will run it and then will become a display along side my
other builds.
I would like to show them at a model engineer show in the future , just because these shows
are dying out as not enough young people coming through. I am in my 50's and feel like a kid
when I go to these shows, most of the people I talk to call me 'young man'.

[iansoady]

Yes, those model engineering shows are fantastic. I go to the one near Leamington occasionally and am blown away by the quality of some of the work.

[rodbargee]

Awsome stuff here, I built a twin cyl, steam engine when I was 16 just a motor and boiler very crude daern't sully this thread with a photo really, stuck it in a nailed together boat, hated woodwork hence the nails, got chucked out of the woodwork dept for not trying.

[kendo57]

Been struggling a bit , I think the lock down is getting to me and I have messed a few
parts up. Might have to take a break and find something else to relieve my stress.
I finished the carb though

So this horrible casting is the carb



So I set about boring out the float chamber and drilling the carb inlet
This picture illustrates just how much swarf is produced from little machining.



opening out the venture

[kendo57]

The float chamber is actually a dummy , the fuel is fed directly to the main jet.
This was turned out of stainless then a fuel inlet pipe was soldered on

This is the set up before soldering



I turned a knurled cap to hold the metering needle



So here are the parts

You can see the main jet plus metering needle , this was loctited into the knurled cap.
A brass throttle butterfly and shaft
Brass cover and screw for the float bowl

[kendo57]

Finished carb in joined to the manifold buy a nylon adaptor

[iansoady]

If there's no float chamber, what stops all the fuel from the tank leaking straight out of the carb? Even if you turn the tap off, the pressure at the carb will change depending on the amount of fuel in the tank (like the old Wal Phillips "injector").

[kendo57]

Your right , the R/C carb I bought for my other engine worked in the same way and dribbled
fuel out of the carb . I think you have to have the fuel fairly level with the carb so you can control
it better with the needle.
I will have a look on some R/C Model sites for some guidance.

[iansoady]

You could get exotic and have a weir type arrangement with a pumped return to the tank. Probably more trouble than it's worth. Otherwise a remote float chamber (like an Amal matchbox) shouldn't be too hard for someone with your skills!

[kendo57]

Knurled and turned a small brass filler cap for the oil



Cut some pieces of brass tube plus a base



Then some silver soldering and i have my filler tube /cap plus a crankcase breather.
The ball bearing goes in the breather before the cap is screwed on to act as a one way valve

[hilldweller]

When it's finished it might be something like this.

My question is, why don't the pistons fill up with oil ?

https://en.wikipedia.org/wiki/De_Havilland_Gipsy_Major

[kendo57]

When it's finished it might be something like this.

My question is, why don't the pistons fill up with oil ?

https://en.wikipedia.org/wiki/De_Havilland_Gipsy_Major

That engine is the same as mine but modified to run upside down . They sealed the engine
with push rod tubes and rocker covers ect .
I am no expert but i believe the oil did fill the pistons then get thrown out when started,
they welded baffles into the sump and fitted a scavenging pump to collect oil.
The engines were inverted so the pilots could have uninterrupted forward vision [you probably
new that]

[hilldweller]

The engines were inverted so the pilots could have uninterrupted forward vision [you probably
new that]

I actually thought the engine was inverted so the crank was high up to take a big prop direct onto the crank, so I got that wrong.

A long time ago I did have two lessons in a Chipmunk, from Woodvale, I remember we had to sit with the engine running until the oil reached a certain temperature before we could taxi.

[kendo57]

Spark plugs,, the heads are tapped 1/4 32tpi which is a common size for R/C engine glow plugs.
There are a few companies making spark plugs for this thread size but they are quite expensive
and my engine needs eight.
So i did some research on making some,, it seems the problem has always been finding an insulator
to replace the ceramic on a full size plug but modern materials are now available which can be machined.
I went for a material called Corian which is used for kitchen worktops, luckily off cuts can be had on EBay.

So a few minutes on Ebay and i have a Corian off cut , 8mm hex steel bar and some 1mm tungsten welding
rods for the electrode. I also broke up a full size plug just for referance.



First i put the 8mm hex in the lathe and turned a small section round for the electrode then turned a
1/4 round for the threaded section and a little more round for the body . I would have threaded them
at this stage but my Die was still in the post.



I then machined the electrode on the mill



Followed by an undercut with a small Dremmel blade

[Lutin]

Making your own spark plugs.

Brilliant!

[kendo57]

The plug body is then put back into the lathe in reverse and a flat bottomed 4mm mill bit is used to
drill out the body just deep enough to brake through to the undercut but not touch the electrode.



This is my lathe setup with a cheap digital calliper fastened to my tail chuck so i can drill accurately
to depth




After the 4mm hole was drilled through, the body was counterbored 6mm to about half way.
This counterbore left a taper seat for the insulator to seal against.
A piece of Corian was cut and turned to the correct size and shape for a snug fit into the body



The Corian insulators are drilled through the centre 1mm to accept the electrode and then
loctited into the body . I also left a small lip on the plug body which was pressed over to seal
the insulator in, i made a small die to fold the lip over but forgot to take a pic.



You can see i have threaded them as my Die turned up and i cut the tungsten rods to length
and soldered a m2 brass thread to the top.

The tungsten electrode is then loctited into the insulator and the brass thread trimmed

[Dodgy69]

Very very interesting read, excellent.